Ophthalmologic apparatus and method of controlling the same

ABSTRACT

An ophthalmologic apparatus of embodiments includes an OCT unit, an acquisition unit, and a specifying unit. The OCT unit is configured to acquire a tomographic image of a subject&#39;s eye using optical coherence tomography. The acquisition unit is configured to acquire a front image of the subject&#39;s eye. The specifying unit is configured to specify shape of a tissue of the subject&#39;s eye based on the tomographic image acquired by the OCT unit and the front image acquired by the acquisition unit.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromU.S. Provisional Application No. 62/793,044, filed Jan. 16, 2019; theentire contents of which are incorporated herein by reference.

FIELD

Embodiments according to present invention described herein relate to anophthalmologic apparatus and a method of controlling the same.

BACKGROUND

In recent years, as one of the causes of myopia progress, a possibilitythat myopia may progress as the retina tries to extend to the back sidedue to the focal point of the peripheral visual field being on the backside (sclera side) of the retinal surface has been reported (forexample, Earl L. Smith et al, “Relative peripheral hyperoptic defocusalters central refractive development in infant monkeys”, VisionResearch, September 2009, 49 (19), pp. 2386-2392).

In order to suppress such myopia progress, eyeglasses and contactlenses, which move the focal position of the central visual field to thenear side (cornea side) by increasing the refractive power of theperipheral visual field, have been developed. Further, refractivesurgeries such as the wavefront-guided LASIK, which is performed basedon wavefront aberration measured in advance, are also performed.Therefore, in such high-performance refractive correction, measuringaccurately the refractive power of the peripheral visual field isrequired.

In addition, some types of eyeball shape have been ascertained (forexample, Pavan K Verkicharla et al. “Eye shape and retinal shape, andtheir relation to peripheral refraction”, Ophthalmic & PhysiologicalOptics, 32 (2012), pp. 184-199).

Such eyeball shapes also include types of shapes common to people withmyopia and the like. It is considered effective to measure the change ofthe shape with myopia progress and to feed back the measurement resultto ways to cope with the myopia progress.

SUMMARY

One aspect of some embodiments is an ophthalmologic apparatuscomprising: an OCT unit configured to acquire a tomographic image of asubject's eye using optical coherence tomography; an acquisition unitconfigured to acquire a front image of the subject's eye; and aspecifying unit configured to specify shape of a tissue of the subject'seye based on the tomographic image acquired by the OCT unit and thefront image acquired by the acquisition unit.

Another aspect of some embodiments is a method of controlling anophthalmologic apparatus, the method comprising: a tomographic imageacquisition step that acquires a tomographic image of a subject's eyeusing optical coherence tomography; a front image acquisition step thatacquires a front image of the subject's eye; and a specifying step thatspecifies shape of a tissue of the subject's eye based on thetomographic image acquired in the tomographic image acquisition step andthe front image acquired in the front image acquisition step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an example of theconfiguration of an ophthalmologic apparatus according to theembodiments.

FIG. 2 is a schematic diagram illustrating an example of theconfiguration of the ophthalmologic apparatus according to theembodiments.

FIG. 3 is a schematic diagram illustrating an example of theconfiguration of the ophthalmologic apparatus according to theembodiments.

FIG. 4 is a schematic diagram illustrating an example of theconfiguration of the ophthalmologic apparatus according to theembodiments.

FIG. 5 is a schematic diagram illustrating an example of theconfiguration of the ophthalmologic apparatus according to theembodiments.

FIG. 6 is a schematic diagram for explaining an operation of theophthalmologic apparatus according to the embodiments.

FIG. 7 is a schematic diagram for explaining an operation of theophthalmologic apparatus according to the embodiments.

FIG. 8 is a schematic diagram for explaining an operation of theophthalmologic apparatus according to the embodiments.

FIG. 9 is a flowchart illustrating an example of the operation of theophthalmologic apparatus according to the embodiments.

FIG. 10 is a flowchart illustrating an example of the operation of theophthalmologic apparatus according to the embodiments.

FIG. 11 is a schematic diagram for explaining an operation of theophthalmologic apparatus according to the embodiments.

FIG. 12 is a schematic diagram for explaining an operation of theophthalmologic apparatus according to the embodiments.

FIG. 13 is a flowchart illustrating an example of the operation of theophthalmologic apparatus according to a modification example of theembodiments.

DETAILED DESCRIPTION

In general ophthalmologic apparatuses, a fixation target is projectedonto a measurement optical axis. Thereby, the refractive power near thefovea of the retina is measured. In this case, taking into account theshape of the tissue in the fundus or the like (shape of the eyeball), itis possible to obtain the refractive power of the peripheral visualfield from the refractive power of the vicinity of the fovea.

However, when a tomographic image of a subject's eye is acquired usingoptical coherence tomography for the purpose of measuring the shape ofthe tissue in the fundus or the like, it is difficult to acquire thetomographic image with high reproducibility due to the amount ofmisalignment of alignment by the motion of the eye.

According to some embodiments of the present invention, a new techniquefor specifying shape of a tissue of a subject's eye with highreproducibility and high accuracy can be provided.

Referring now to the drawings, exemplary embodiments of anophthalmologic apparatus and a method of controlling the ophthalmologicapparatus according to the present invention are described below. Any ofthe contents of the documents cited in the present specification andarbitrary known techniques may be applied to the embodiments below.

The ophthalmologic apparatus according to embodiments is capable ofacquiring a tomographic image of a subject's eye by performing opticalcoherence tomography (OCT) on the subject's eye, and specifying(extrapolating, predicting) a true shape of a tissue of the subject'seye by correcting the tomographic image (or shape data obtained by thetomographic image) based on a front image of the subject's eye. Thetomographic image of the subject's eye is acquired using an opticalsystem for performing OCT. The front image of the subject's eye isacquired using one or more anterior segment cameras provided separatelyfrom the above optical system.

The ophthalmologic apparatus according to some embodiments is configuredto specify a displacement (amount of alignment error, direction) of theabove optical system with respect to the subject's eye by analyzing thefront image (anterior segment image), and to specify the shape of thetissue based on the specified displacement. The ophthalmologic apparatusaccording to some embodiments is configured to specify a displacement(amount of alignment error, direction) of the above optical system withrespect to the subject's eye from a photographing range or a position offlare by analyzing the fundus image OR fundus image), and to specify theshape of the tissue based on the specified displacement. In theophthalmologic apparatus according to some embodiments, the shape of thetissue is specified by one-dimensional, two-dimensional, orthree-dimensional shape data of a predetermined layer region obtained byanalyzing the tomographic image. For example, the ophthalmologicapparatus obtains a coordinate position in a predetermined coordinatesystem corresponding to a position on ray of measurement light(coordinate position in a measurement coordinate system (OCT coordinatesystem)) by performing ray tracing processing on the basis of adisplacement with respect to a measurement optical axis (optical axis ofthe above optical system) on the measurement light for performing OCT.And the ophthalmologic apparatus corrects the tomographic image or theshape data representing the shape of the tissue obtained from thetomographic image based on the obtained coordinate position. Examples ofthe predetermined coordinate system include an optical model coordinatesystem (physical coordinate system) used in the above ray tracingprocessing, and a coordinate system having a substantially lowcorrelation with the displacement of the above optical system withrespect to the subject's eye such as a measurement coordinate system inwhich the above displacement is substantially zero.

By specifying the shape of the tissue of the subject's eye from thetomographic image corrected as described above or the shape datacorrected as described above, the influence of an amount of misalignmentof alignment (amount of alignment error) of the subject's eye withrespect to the optical system for performing OCT can be reduced and theshape of the tissue of the subject's eye can be specified with highreproducibility and high accuracy.

Examples of the shape of the tissue in the subject's eye include a shapeof a tissue in the anterior segment, a shape of a tissue in theposterior segment, and the like. Example of the shape of the tissue inthe anterior segment include a shape of a cornea, a shape of an iris, ashape of a crystalline lens, a shape of a ciliary body, a shape of aciliary zonule, a shape of an angle, and the like. Examples of the shapeof the tissue in the posterior segment include a shape of the fundus (apredetermined layer region in the fundus), and the like. Hereinafter,the shape of the fundus will be described as an example of the shape ofthe tissue according to the embodiments. However, the embodimentsdescribed after can be applied to the shape of any site of the eyeballother than the fundus. Further, in the following embodiments, shape datarepresenting the shape of the fundus may be referred to as a shapeprofile. The shape profile is data representing a change in shape in apredetermined one-dimensional direction, a predetermined two-dimensionaldirection, or a predetermined three-dimensional direction.

The ophthalmologic apparatus according to some embodiments calculates(extrapolates, estimates) a refractive power of a peripheral regionoutside a region including a fovea in the fundus using the shape of thefundus specified as described above. For example, the ophthalmologicapparatus calculates the refractive power of the peripheral regionoutside the region including the fovea, based on a refractive power ofthe region including the fovea of the subject's eye and the specifiedshape of the fundus.

The ophthalmologic apparatus according to the embodiments can calculatethe refractive power of the above region using parameters of an eyeballmodel such as a known schematic eye (parameters representing opticalcharacteristics of the eyeball). Examples of the parameter include axiallength data, anterior chamber depth data, crystalline lens data(curvature of crystalline lens, thickness of crystalline lens, or thelike) representing a shape of a crystalline lens, corneal shape data(corneal curvature radius, corneal thickness, or the like), and thelike. The ophthalmologic apparatus can build (form) a new eyeball modelby replacing a part of the parameters of the eyeball model with themeasured value of the subject's eye, and calculate the refractive powerof the above region using the built new eyeball model. In someembodiments, the above parameter is obtained from an electronic healthrecord system, a medical image archiving system, an external apparatus,or the like.

A method of controlling the ophthalmologic apparatus according to theembodiments includes one or more steps for realizing the processingexecuted by a processor (computer) in the ophthalmologic apparatusaccording to the embodiments. A program according to the embodimentscauses the processor to execute each step of the method of controllingthe ophthalmologic apparatus according to the embodiments.

The term “processor” as used herein refers to a circuit such as, forexample, a central processing unit (CPU), a graphics processing unit(GPU), an application specific integrated circuit (ASIC), and aprogrammable logic device (PLD). Examples of PLD include a simpleprogrammable logic device (SPLD), a complex programmable logic device(CPLD), and a field programmable gate array (FPGA). The processorrealizes the function according to the embodiments, for example, byreading out a computer program stored in a storage circuit or a storagedevice and executing the computer program.

In this specification, images acquired using OCT may be collectivelyreferred to as “OCT images”. Further, a measuring action for forming anOCT image is sometimes referred to as an OCT measurement. Data acquiredby performing OCT scan is sometimes referred to as scan data.

Hereinafter, a case will be described where the ophthalmologic apparatusaccording to the embodiments is configured to acquire the tomographicimage of the subject's eye by performing OCT on the subject's eye and toacquire the front image of the anterior segment of the subject's eye.However, the ophthalmologic apparatus according to the embodiments maybe configured to acquire scan data (OCT data), the tomographic image,the shape profile described after, the front image, or the like from anexternal ophthalmologic apparatus.

The ophthalmologic apparatus according to some embodiments includes anOCT apparatus and is configured to perform registration between thesubject's eye and an optical system for performing OCT. Theophthalmologic apparatus according to some embodiments further includesan objective refractometry apparatus. The ophthalmologic apparatusaccording to some embodiments includes a device (communicationinterface, input/output interface, etc.) that receives data from anexternal apparatus or a recording medium.

That is, the ophthalmologic apparatus according to the embodiments maybe, for example, any one of the following: (A) an inspection apparatusthat includes an objective refractometry apparatus (refractometry unit)and an OCT apparatus (OCT unit): (B) an inspection apparatus that doesnot include an objective refractometry apparatus (refractometry unit)but includes an OCT apparatus (OCT unit): (C) an information processingapparatus that includes neither an objective refractometry apparatus(refractometry unit) nor an OCT apparatus (OCT) unit.

Hereinafter, the left/right direction (i.e., horizontal direction) whichis orthogonal to the optical axis of the optical system of theophthalmologic apparatus is regarded as the x direction, the up/downdirection (i.e., vertical direction) which is orthogonal to the axis isregarded as the y direction, and the optical axis direction (i.e., depthdirection, front-back direction) is regarded as the z direction.

<Configuration>

FIGS. 1 to 5 illustrate examples of the configuration of theophthalmologic apparatus according to the embodiments. FIG. 1 is aschematic block diagram illustrating an example of the configuration ofthe ophthalmologic apparatus according to the embodiments. FIG. 2 showsa functional block diagram representing a configuration example of adata processor 70 in FIG. 1. FIG. 3 shows a functional block diagramrepresenting a configuration example of an alignment processor 71 inFIG. 2. FIG. 4 shows a functional block diagram representing aconfiguration example of a correction unit 731 in FIG. 2. FIG. 5 shows afunctional block diagram representing a configuration example of acalculator 74 in FIG. 2.

The ophthalmologic apparatus 1 is an inspection apparatus that includesan objective refractometry apparatus (refractometry unit) and an OCTapparatus (OCT unit). The ophthalmologic apparatus 1 includes ameasurement unit 10, a control processor 50, a movement mechanism 90,and an imaging unit 100. The measurement unit 10 includes arefractometry unit 20, an OCT unit 30, an alignment light projectionunit 40, and beam splitters BS1 and B2. The control processor 50includes an image forming unit 60, a data processor 70, and a controller80.

(Refractometry Unit 20)

The refractometry unit 20 objectively measures a refractive power of asubject's eye E under the control of the controller 80. Therefractometry unit 20 includes an optical system provided with one ormore optical members for performing objective refractometry. Therefractometry unit 20 has the same configuration as a knownrefractometer, for example. An exemplary refractometer (not shown in thefigure) includes a projection system and a light reception system asdisclosed in Japanese Unexamined Patent Application Publication No.2016-077774.

A projection system of the refractometry unit 20 is configured toproject light emitted from a light source onto a fundus Ef of thesubject's eye E. The projection system projects the light from the lightsource onto the fundus Ef through a collimate lens, a focusing lens, arelay lens, a pupil lens, a perforated prism, a decentered prism(eccentric prism), an objective lens, and the like, for example.

A light reception system of the refractometry unit 20 projects reflectedlight from the fundus Ef onto an imaging element through the objectivelens, the decentered prism, the perforated prism, other pupil lenses,other relay lenses, another focusing lens, a conical prism, an imaginglens, and the like. Thereby, a ring pattern image formed on an imagingsurface of the imaging element is detected.

In some embodiments, the refractometry unit 20 is configured to projectring-shaped light onto the fundus Ef and to detect the ring patternimage formed by the reflected light from the fundus Ef. In someembodiments, the refractometry unit 20 is configured to project brightspot onto the fundus Ef, to convert the reflected light from the fundusEf into ring-shaped light, and to detect the ring pattern image formedby the converted ring-shaped light.

(OCT Unit 30)

The OCT unit 30 acquires OCT data (scan data) by applying OCT scan tothe subject's eye E under the control of the controller 80. The OCT datamay be interference signal data, reflection intensity profile dataobtained by applying Fourier transformation to the interference signaldata, image data obtained by imaging the reflection intensity profiledata.

The OCT method that can be performed by the OCT unit 30 is typicallyFourier domain OCT. Fourier domain OCT may be either spectral domain OCTor swept source OCT. The swept source OCT is a method that splits lightfrom a wavelength tunable light source into measurement light andreference light; superposes returning light of the measurement lightprojected onto the subject's eye from the subject's eye with thereference light to generate interference light; detects the interferencelight with an optical detector; and applies the Fourier transformationetc. to detection data (interference signal data) acquired in accordancewith the sweeping of wavelengths and the scanning of the measurementlight to form reflection intensity profile data. On the other hand, thespectral domain OCT is a method that splits light from a low coherencelight source (broadband light source) into measurement light andreference light; superposes returning light of the measurement lightprojected onto the subject's eye from the subject's eye with thereference light to generate interference light; detects the spectraldistribution of the interference light with a spectrometer; and appliesthe Fourier transformation etc. to detection data (interference signaldata) detected by the spectrometer to form reflection intensity profiledata. That is, the swept source OCT is an OCT method for acquiring thespectral distribution by time division, and the spectral domain OCT isan OCT method for acquiring the spectral distribution by space division.

The OCT unit 30 includes an optical system provided with one or moreoptical members for performing OCT measurement. The OCT unit 30 has thesame configuration as a known OCT apparatus, for example. An exemplaryOCT apparatus (not shown in the figure) includes a light source, aninterference optical system, a scan system, and a detection system asdisclosed in Japanese Unexamined Patent Application Publication No.2016-077774.

Light output from the light source is split into the measurement lightand the reference light by the interference optical system. Thereference light is guided by a reference arm. The measurement light isprojected onto the subject's eye E (for example, the fundus Ef) througha measurement arm. The measurement arm is provided with the scan system.The scan system includes, for example, an optical scanner and is capableof deflecting the measurement light one-dimensionally ortwo-dimensionally. The optical scanner includes one or more galvanoscanners. The scan system deflects the measurement light according to apredetermined scan mode.

The controller 80 described after can control the scan system accordingto the scan mode. Examples of the scan mode include line scan, rasterscan (three-dimensional scan), circle scan, concentric scan, radialscan, cross scan, multi cross scan, spiral scan, and the like. The linescan is a scan pattern along a linear trajectory. The raster scan is ascan pattern consisting of a plurality of line scans arranged parallelto one another. The circle scan is a scan pattern along a circulartrajectory. The concentric scan is a scan pattern consisting of aplurality of circle scans arranged concentrically. The radial scan is ascan pattern consisting of a plurality of line scans arranged radially.The cross scan is a scan pattern consisting of two line scans arrangedorthogonal to one another. The multi cross scan is a scan patternconsisting of two line scan groups (for example, each groups includesfive lines parallel to one another) orthogonal to one another. Thespiral scan is a scan pattern extending in a spiral manner from thecenter.

The measurement light projected onto the fundus Ef is scattered andreflected at various depth positions (layer boundaries, etc.) of thefundus Ef. The returning light of the measurement light from thesubject's eye E is combined with the reference light by the interferenceoptical system. The returning light of the measurement light and thereference light generates the interference light according to theprinciple of superposition. This interference light is detected by thedetection system. The detection system typically includes thespectrometer in case of spectral domain OCT. The detection systemtypically includes a balanced photodiode and a data acquisition system(DAQ) in case of swept source OCT.

(Alignment Light Projection Unit 40)

The alignment light projection unit 40 projects alignment light forperforming registration (position matching) between the subject's eye Eand the measurement unit 10 (OCT unit, the optical system of theapparatus). The alignment light projection unit 40 includes an alignmentlight source and a collimator lens. An optical path of the alignmentlight projection unit 40 is coupled with an optical path of therefractometry unit 20 by the beam splitter BS2. Light emitted from thealignment light source passes through the collimator lens, is reflectedby the beam splitter BS2, and is projected onto the subject's eye Ethrough the optical path of the refractometry unit 20.

In some embodiments, as disclosed in Japanese Unexamined PatentApplication Publication No. 2016-077774, the reflected light from thecornea Ec (anterior segment) of the subject's eye E is guided to thelight reception system of the refractometry unit 20 through the opticalpath of the refractometry unit 20.

An image (bright spot image) based on the reflected light by the corneaEc of the subject's eye E is included in the anterior segment imageacquired by the imaging unit 100. For example, the control processor 50controls the display unit (not shown in Figure) to display an alignmentmark and the anterior segment image including the bright spot image onthe display screen of the display unit. In the case of performing XYalignment (registration) (alignment in vertical and horizontaldirections) manually, a user can perform an operation for moving theoptical system so as to guide the bright spot image in the alignmentmark. In the case of performing Z alignment (alignment in front-backdirection) manually, a user can perform the operation for movement ofthe optical system while referring to the anterior segment imagedisplayed on the display screen of the display unit. In the case ofperforming alignment automatically, the controller 80 controls themovement mechanism 90 to relatively move the measurement unit 10(optical system) with respect to the subject's eye E so as to cancel thedisplacement between the alignment mark and the position of the brightspot image. Further, the controller 80 can control the movementmechanism 90 to move the measurement unit 10 (optical system) withrespect to the subject's eye E so as to satisfy a predeterminedalignment completion condition based on a position of a predeterminedsite (for example, pupil center position) of the subject's eye E and theposition of the bright spot image.

(Beam Splitter BS1)

The beam splitter BS1 coaxially couples the optical path of the opticalsystem (interference optical system, etc.) of the OCT unit 30 with theoptical path of the optical system (projection system and lightreception system) of the refractometry unit 20. For example, a dichroicmirror is used as the beam splitter BS1.

(Beam splitter BS2)

The beam splitter BS2 coaxially couples the optical path of the opticalsystem of the alignment light projection unit 40 with the optical pathof the optical system (projection system and light reception system) ofthe refractometry unit 20. For example, a half mirror is used as thebeam splitter BS2.

In some embodiments, the ophthalmologic apparatus 1 has a function(fixation projection system) that presents a fixation target, which isused for guiding a visual line of the subject's eye, to the subject'seye E under the control of the controller 80. The fixation target may bean internal fixation target presented to the subject's eye E or anexternal fixation target presented to the fellow eye. In someembodiments, an optical path of the fixation projection system and theoptical path of the interference optical system of the OCT unit 30 areconfigured to coaxially coupled by an optical path coupling member (forexample, beam splitter) arranged between the OCT unit 30 and the beamsplitter BS1.

A projection position of the fixation target in the fundus Ef projectedby the fixation target projection system can be changed under thecontrol of the controller 80. In some embodiments, the fixation targetis projected onto the measurement optical axes of coaxially coupled theoptical system of the refractometry unit 20 and the optical system ofthe OCT unit 30. In some embodiments, the fixation target is projectedat a position deviated from the measurement optical axis on the fundusEf.

(Imaging Unit 100)

The imaging unit 100 includes one or more anterior segment cameras forimaging the anterior segment of the subject's eye E. The imaging unit100 acquires the anterior segment image which is the front image of thesubject's eye E. In some embodiments, at least one anterior segmentillumination light source (infrared light source or the like) isprovided in the vicinity of the one or more anterior segment cameras.For example, for each anterior segment cameras, the anterior segmentillumination light source is provided in the upper vicinity and thelower vicinity of the anterior segment camera, respectively.

The ophthalmologic apparatus 1 can perform registration of themeasurement unit 10 (optical system) with respect to the subject's eye Eusing the front image acquired by the imaging unit 100. In someembodiments, the ophthalmologic apparatus 1 specifies athree-dimensional position of the subject's eye E by analyzing the frontimage acquired by imaging the anterior segment of the subject's eye E,and performs registration by relatively moving the measurement unit 10based on the specified three-dimensional position. In some embodiments,the ophthalmologic apparatus 1 performs registration so as to cancel thedisplacement between a characteristic position of the subject's eye Eand a position of the image formed by the alignment light projected bythe alignment light projection unit 40.

As described above, the imaging unit 100 includes one or more anteriorsegment cameras. In case that the imaging unit 100 includes a singleanterior segment camera, the ophthalmologic apparatus 1 analyzes theacquired front image, and specifies a two-dimensional position of thesubject's eye E in a plane orthogonal to the optical axis of themeasurement unit 10 (plane defined by the horizontal direction (Xdirection) and the vertical direction (Y direction)). In this case, thealignment optical system for specifying a position of the subject's eyeE in the optical axis direction of the measurement unit 10 is providedin the ophthalmologic apparatus 1. Examples of such an alignment opticalsystem includes an optical system of an optical lever system asdisclosed in Japanese Unexamined Patent Application Publication No.2016-077774. The ophthalmologic apparatus 1 can specify thethree-dimensional position of the subject's eye E from the position ofthe subject's eye in the (measurement) optical axis of the measurementunit 10 and the above two-dimensional position, using such alignmentoptical system like this.

In case that the imaging unit 100 includes two or more anterior segmentcameras, two or more anterior segment cameras photograph the anteriorsegment of the subject's eye E from different directions. The two ormore anterior segment cameras can substantially simultaneouslyphotograph the anterior segment from two or more different directions.The phrase “substantially simultaneously” indicates that the deviationin photography timings at a level where the eye movement is negligibleis allowed in the photography with two or more anterior segment cameras.Thereby, images of the subject's eye E located in substantially the sameposition (orientation) can be acquired by the two or more anteriorsegment cameras. The ophthalmologic apparatus 1 analyzes the frontimages of the subject's eye E, specifies the characteristic position ofthe subject's eye E, and specifies the three-dimensional position of thesubject's eye E from the positions of the two or more anterior segmentcameras and the characteristic position.

Photography using the two or more anterior segment cameras may be movingimage photography or still image photography. In the case of movingimage photography, substantially simultaneous photography of theanterior segment as described above can be realized by performingcontrol for synchronizing photography start timings, controlling theframe rates or the capture timings of respective frames, or the like. Onthe other hand, in the case of still image photography, this can berealized by performing control for synchronizing photography timings.

In the following, it is assumed that the imaging unit 100 includes twoanterior segment cameras. Each of the two anterior segment cameras islocated at a position off the measurement optical axis (optical axis ofthe OCT unit 30) as disclosed in Japanese Unexamined Patent ApplicationPublication No. 2013-248376. In some embodiments, one of the twoanterior segment cameras is an imaging element in the light receptionsystem of the refractometry unit 20.

(Control Processor 50)

The control processor 50 performs various calculations and variouscontrols for operating the ophthalmologic apparatus 1. The controlprocessor 50 includes one or more processors and one or more storagedevices. Examples of the storage device include random access memory(RAM), read only memory (ROM), hard disk drive (HDD), solid state drive(SSD), and the like. The storage device stores various computerprograms. The calculation and control according to the present examplesare realized by operating the processor based on it.

(Image Forming Unit 60)

The image forming unit 60 forms an image (tomographic image, etc.) ofthe subject's eye E based on the scan data acquired by performing OCT onthe subject's eye E. The image forming unit 60 builds OCT data(typically, image data) based on detection data detected by thedetection system of the OCT unit 30. The image forming unit 60, similarto conventional OCT data processing, builds the reflection intensityprofile data in A line (path of the measurement light in the subject'seye E), by applying filter processing, fast Fourier transformation(FFT), and the like to the detection data. In addition, the imageforming unit 60 builds the image data of each A line (A scan data) byapplying image processing (image expression) to this reflectionintensity profile data. In some embodiments, the function of the imageforming unit 60 is realized by a processor.

In some embodiments, at least part of the function of the image formingunit 60 is provided in the OCT unit 30.

(Data Processor 70)

The data processor 70 executes various data processing. The dataprocessor 70 can build (form) B scan data by arranging a plurality of Ascan data according to the scan mode performed by the scan system. Thedata processor 70 can build stack data by arranging a plurality of Bscan data according to the scan mode performed by the scan system. Thedata processor 70 build volume data (voxel data) from the stack data.The data processor 70 can render the stack data or the volume data.Examples of rendering method include volume rendering, multi-planarreconstruction (MPR), surface rendering, projection, and the like.

The data processor 70 can execute processing for performing registrationof the measurement unit 10 with respect to the subject's eye E. Examplesof the processing for performing registration include analysisprocessing of the front image of the subject's eye E acquired using theimaging unit 100, calculation processing of the position of thesubject's eye E, calculation processing of the displacement of themeasurement unit 10 with respect to the subject's eye E, and the like.

In addition, the data processor 70 can specify a displacement betweenthe subject's eye E after registration (alignment) and the measurementunit 10, and generate shape data (shape profile) representing the shapeof the fundus Ef of the subject's eye E based on the specifieddisplacement. Further, the data processor 70 can calculate refractivepower of a peripheral region of a region including a fovea of thesubject's eye E using the specified shape of the subject's eye E.

As shown in FIG. 2, such as the data processor 70 includes an alignmentprocessor 71, a displacement specifying unit 72, an analyzer 73, and acalculator 74.

(Alignment Processor 71)

The alignment processor 71 executes processing for performingregistration of the measurement unit 10 with respect to the subject'seye E. In some embodiments, the alignment processor 71 correctsdistortion of the photographic images captured by the anterior segmentcameras, and executes processing for performing above registration usingthe captured photographic image(s) whose distortion has (have) beencorrected. In this case, the alignment processor 71 corrects thedistortion of the photographic image(s) based on the aberrationinformation stored in a storage unit provided in the control processor50 or the data processor 70. This processing is performed by, forexample, known image processing technology based on a correction factorfor correcting distortion aberration.

As shown in FIG. 3, the alignment processor 71 includes a Purkinje imagespecifying unit 71A, a pupil center specifying unit 71B, and a movementtarget position determining unit 71C.

(Purkinje Image Specifying Unit 71A)

By projecting the alignment light onto the anterior segment of thesubject's eye E using the alignment light projection unit 40, a Purkinjeimage is formed. The Purkinje image is formed in a position displacedfrom the corneal apex in the optical axis direction (z direction) byhalf of the radius of the corneal curvature.

The anterior segment onto which the alignment light is projected issubstantially simultaneously photographed by the two anterior segmentcameras. The Purkinje image specifying unit 71A specifies the Purkinjeimage (image region corresponding to the Purkinje image) by analyzingeach of the two photographic images substantially simultaneouslyacquired using the two anterior segment cameras. This specifyingprocessing includes, for example as in the conventional case, athreshold processing related to a pixel value for searching for a brightspot (pixel having high brightness) corresponding to the Purkinje image.Thereby, the image regions in the photographic images corresponding tothe Purkinje image are specified.

The Purkinje image specifying unit 71A can obtain a position of arepresentative point in the image region corresponding to the Purkinjeimage. The representative point may be a center point or a center ofgravity point of the image region, for example. In this case, thePurkinje image specifying unit 71A can obtain an approximate circle oran approximate ellipse of the periphery of the image region, and canobtain the center point or the center of gravity point of theapproximate circle or the approximate ellipse.

Each of the two photographic images is an image obtained byphotographing the anterior segment from a diagonal direction. In each ofthe photographic images, a pupil region and a Purkinje image aredepicted. The Purkinje image specifying Unit 71A specifies the Purkinjeimages in the two photographic images.

Here, the two photographic images are images obtained by photographingfrom directions different from the optical axis of the measurement unit10 (objective lens). When XY alignment is substantially matched, thePurkinje images in the two photographic images are formed on the opticalaxis of the measurement unit 10.

Visual angles (angles with respect to the optical axis of themeasurement unit 10) of the two anterior segment cameras are known andthe photographing magnification is also known. Thereby, the relativeposition (three-dimensional position in actual space) of the Purkinjeimage formed in the anterior segment with respect to the ophthalmologicapparatus 1 (imaging unit 100) can be obtained based on the positions ofthe Purkinje images in the two photographic images.

Further, the relative position between the characteristic position ofthe subject's eye E and the Purkinje image formed in the anteriorsegment can be obtained based on the relative position (misalignmentamount) between the characteristic position of the subject's eye E andthe position of the Purkinje image in each of the two photographicimages.

The Purkinje image specifying unit 71A specifies the position of thePurkinje image specified as above. The position of the Purkinje imagemay include at least a position in the x direction (x coordinate value)and a position in the y direction (y coordinate value), or may furtherinclude a position in the z direction (z coordinate value).

(Pupil Center Specifying Unit 71B)

The pupil center specifying unit 71B specifies a position in thephotographic image corresponding to a predetermined characteristicposition of the anterior segment by analyzing each of photographicimages obtained by the anterior segment cameras or the images correctedfor distortion aberration. In the present embodiment, the pupil centerof the subject's eye E is specified. It should be noted that the centerof gravity of the pupil may be obtained as the pupil center. It is alsopossible to configure such that the characteristic position other thanthe pupil center (the center of gravity of the pupil) is specified.

The pupil center specifying unit 71B specifies the image region (pupilregion) corresponding to the pupil of the subject's eye E based on thedistribution of pixel values (luminance values etc.) in the photographicimage. Generally, the pupil is represented with lower luminance comparedto other sites, and therefore, the pupil region may be specified bysearching an image region with low luminance. At this time, the pupilregion may be specified by taking the shape of the pupil intoconsideration. That is, it is possible to configure such that the pupilregion is specified by searching for a substantially circular imageregion with low luminance.

Next, the pupil center specifying unit 71B specifies the center positionof the specified pupil region. As mentioned above, the pupil issubstantially circular. Accordingly, by specifying the contour of thepupil region and then specifying the center position of an approximateellipse of this contour, this may be used as the pupil center. Instead,by obtaining the center of gravity of the pupil region, this center ofgravity may be used as the pupil center.

Note that, even when other characteristic positions are employed, theposition of the characteristic position can be specified based on thedistribution of pixel values in the photographic image in the samemanner as mentioned above.

The pupil center specifying unit 71B specifies the three-dimensionalposition of the pupil center of the subject's E, based on the positionsof the two anterior segment cameras (and the photographingmagnification) and the positions of the specified pupil center in thetwo photographic images.

For example, the resolution of photographic images obtained by the twoanterior segment cameras is expressed by the following expressions.xy resolution(planar resolution): Δxy=H×Δp/fz resolution(depth resolution): Δz=H×H×Δp/(B×f)

Here, the distance (base line length) between the two anterior segmentcameras is represented as “B”, the distance (photographing distance)between the base line of the two anterior eye cameras and the pupilcenter of the subject's eye E is represented as “H”, the distance(screen distance) between each anterior segment camera and its screenplane is represented as “f”, and the pixel resolution is represented as“Δp”.

The pupil center specifying unit 71B applies known trigonometry to thepositions of the two anterior segment cameras (these are known) andpositions corresponding to the pupil center in the two photographicimages, thereby calculating the three-dimensional position of the pupilcenter.

(Movement Target Position Determining Unit 71C)

The movement target position determining unit 71C determines themovement target position of the measurement unit 10 (optical system ofthe apparatus) based on the position of the Purkinje image specified bythe Purkinje image specifying unit 714 and the position of the pupilcenter specified by the pupil center specifying unit 71B. For example,the movement target position determining unit 71C obtains the differencebetween the position of the specified Purkinje image and the position ofthe specified pupil center, and determines the movement target positionso that the obtained difference satisfies a predetermined alignmentcompletion condition.

The controller 80 described after controls the movement mechanism 90based on the movement target position determined by the movement targetposition determining unit 71C.

<Displacement Specifying Unit 72>

The displacement specifying unit 72 specifies a displacement between thesubject's eye E and the measurement unit 10 based on the front image ofthe subject's eye E, after registration (alignment) of the measurementunit 10 with respect to the subject's eye E is completed. Theregistration is performed by controlling the movement mechanism 90 basedon the movement target position determined by the above alignmentprocessor 71.

In some embodiments, the displacement specifying unit 72 specifies thedisplacement between the measurement optical axis of the measurementunit 10, which registration has been performed, and the eyeball opticalaxis of the subject's eye E. The measurement optical axis is an opticalaxis (or the optical axis of the objective lens) of the optical systemat projects the measurement light onto the subject's eye E. The eyeballoptical axis may be an arbitrary axis passing through the eyeball suchas a visual axis, an ocular axis, and the like. In the case that the OCTmeasurement is performed while projecting the fixation light flux ontothe subject's eye E, the eyeball optical axis is the visual axis. Thedisplacement specifying unit 72 can specify the displacement in the xdirection and the y direction with respect to the measurement opticalaxis on the lens surface (or the vicinity thereof) on the subject's eyeE side of the objective lens (not shown) of the measuring unit 10.

(Analyzer 73)

As shown in FIG. 2, the analyzer 73 includes a correction unit 731, alayer region specifying unit 732, and a specifying unit 733. Thecorrection unit 731 corrects the tomographic image of the subject's eyeE based on the displacement specified by the displacement specifyingunit 72. The layer region specifying unit 732 specifies a predeterminedlayer region in the tomographic image corrected by the correction unit731. The specifying unit 733 specifies the shape of the fundus Ef basedon the predetermined layer region specified by the layer regionspecifying unit 732.

(Correction Unit 731)

The correction unit 731 generates an optical system model in OCTmeasurement, based on the displacement of the measurement unit 10 withrespect to the subject's eye E in OCT measurement after registration iscompleted. The correction unit 731 performs ray tracing processing onthe measurement light using the generated optical system model,specifies a pixel position in a predetermined coordinate system (forexample, physical coordinate system) corresponding to a pixel positionin the tomographic image in the OCT coordinate system (measurementcoordinate system), and performs coordinate transformation between thespecified coordinate systems.

As shown in FIG. 4, such the correction unit 731 includes a ray tracingprocessor 731A and a coordinate transforming unit 731B.

FIGS. 6 and 7 show diagrams describing the operation of the correctionunit 731 according to the embodiments. FIG. 6 schematically shows theoptical system model according to the embodiments. In FIG. 6, for thepurpose of illustration, only the x component of displacement isillustrated. FIG. 7 schematically shows the OCT coordinate systemaccording to the embodiments. In FIG. 7, the tomographic image, which isformed based on the scan data using the measurement light incident at adisplacement Δx with respect to the measurement optical axis O of themeasurement unit 10 (OCT unit 30), is illustrated.

First, the correction unit 731 obtains a displacement Δ=(Δx, Δy, Δz)between the position of the pupil center of the subject's eye E and theposition of the Purkinje image, which are acquired by the imaging unit100. Here, the displacement Δ represents the displacement in the OCTcoordinate system. The displacement Δ may be a displacement between theposition of the pupil center of the subject's eye E and the position ofthe Purkinje image, which are obtained by the alignment processor 71after registration is completes. In some embodiments, the displacement Δis (Δx, Δy).

Next, the correction unit 731 generates the optical system model usingthe obtained displacement Δ. The optical system model includes the shapeof the lens system such as the objective lens 11 of the measurement unit10 shown in FIG. 6, the biometric data of the subject's eye E, and thedisplacement Δ. The biometric data includes at least one of the cornealshape data of the subject's eye E, the anterior chamber depth data ofthe subject's eye E, and the axial length data of the subject's eye E.In some embodiments, parameters representing optical characteristics ofknown schematic eyes are applied to the optical system model. In someembodiments, an aplanatic ideal optical system is applied to the opticalsystem model as the lens system.

The ray tracing processor 731A (correcting unit 731) obtains a positionin the physical coordinate system (x′, y′, z′) shown in FIG. 6corresponding to a position in the OCT coordinate system (x, y, z) shownin FIG. 7, by performing known ray tracing processing using the aboveoptical system model on the measurement light incident at thedisplacement Δ (displacement Δx in FIG. 6) with respect to themeasurement optical axis O. The physical coordinate system is acoordinate system of a three-dimensional space in which the opticalsystem of the apparatus and the subject's eye E are disposed. The aboveoptical system model is defined in the physical coordinate system.Thereby, this make it possible to recognize to which position in thephysical coordinate system the pixel position (for example, pixelpositions p1, p2, p3) of the tomographic image in the z direction, whichis the traveling direction of the measurement light of FIGS. 6 and 7,corresponds. Therefore, it is possible to transform the coordinate fromthe pixel positions of the tomographic image in the OCT coordinatesystem into the pixel positions in the physical coordinate system. Thecoordinate transforming unit 731B can obtain an image in which the shapeof the fundus Ef depicted in the tomographic image represents a trueshape, by similarly performing ray tracing processing on measurementlight incident at other displacements (incident angle).

In some embodiments, a predetermined layer region (for example, retinalpigment epithelium (RPE) layer, OS (outer segments)—RPE boundarysurface, or nerve fiber layer) is specified. And the coordinatetransforming unit 731B performs coordinate transformation describedabove on pixels of the specified image region (or shape profile), andobtains the image representing the true shape of the layer region.

In some embodiments, an OCT coordinate system in which the displacementΔ is substantially zero is used instead of the physical coordinatesystem. In this case, the positions of the pixels of the tomographicimage in the OCT coordinate system formed by scanning with themeasurement light incident at the displacement Δ are transformed intothe pixel positions defined in the OCT coordinate system in which thedisplacement Δ is substantially zero.

In order to simplify the processing performed by such as the correctionunit 731, the ray tracing processor 731 may calculate the relationshipof coordinate transformation in advance for two or more displacements,may obtain two or more reference transformation systems (tableinformation, calculation formula) as correction information, and mayobtain a new transformation system by interpolating the two or morereference transformation systems assuming linearity or knownnonlinearity. In this case, the coordinate transforming unit 731Btransforms the pixel positions of the tomographic image in the OCTcoordinate system shown in FIG. 7 into the pixel positions in a finalcoordinate system specified using the obtained new transformationsystem. That is, the correction unit 731 can correct the tomographicimage or the shape data based on the correction information and thedisplacement specified by the displacement specifying unit 72, thecorrection information being obtained in advance by performing raytracing processing on the basis of the two or more displacements on themeasurement light.

For example, for each of three types of the displacement: Δx=dx(Δy=Δz=0), Δy=dy (Δx=Δz=0), Δz=dz (Δx=Δy=0), the ray tracing processor731A obtains transformation vectors Dx(x, y, z), Dy(x, y, z), and Dz(x,y, z) for transforming from the OCT coordinate system to the finalcoordinate system at each pixel position in advance (See FIG. 8) In caseof the displacement e=(ex, ey, ez) specified by the displacementspecifying unit 72, the coordinate transforming unit 731B can transformthe position (x0, y0, z0) in the OCT coordinate system before correctioninto the position (x1, y1, z1) in the final coordinate system bycalculating (performing linear interpolation) Dx(x, y, z)×ex/dx+Dy(x,y)×ey/dy+Dz(x, y, z)×ez/dz assuming line y.

(Layer Region Specifying Unit 732)

The layer region specifying unit 732 specifies a predetermined layerregion of the fundus Ef by analyzing the tomographic image corrected bythe correcting unit 731. Examples of the layer region of the fundus Efinclude the inner limiting membrane, the nerve fiber layer, the ganglioncell layer, the inner plexiform layer, the inner nuclear layer, theouter plexiform layer, the outer nuclear layer, the external limitingmembrane, the photoreceptor layer, the retinal pigment epithelium layer,the choroid, the sclera, the boundary surfaces of each layer region, andthe like.

Processing of specifying the predetermined layer region from thetomographic image typically includes segmentation processing. Thesegmentation processing is known processing for specifying a partialregion in a tomographic image. The layer region specifying unit 732performs, for example, segmentation processing based on a brightnessvalue of each pixel in the tomographic image. That is, each of the layerregions of the fundus Ef has a characteristic reflectance, and imageregions corresponding to these layer regions also have characteristicbrightness values. The layer region specifying unit 732 can specify atarget image region (layer region) by performing segmentation processingbased on these characteristic brightness values.

The layer region specifying unit 732 outputs data representing the shapeof the specified predetermined layer region as the shape profile of thelayer region. In some embodiments, the shape profile is one-dimensional,two-dimensional, or three-dimensional shape data representing a changein the shape of the fundus Ef in at least one direction of the x′direction, the y′ direction, and the z′ direction.

For example, the layer region specifying unit 732 can specify theretinal pigment epithelium layer (or OS-RPE boundary surface).

(Specifying Unit 733)

The specifying unit 733 specifies the shape of the fundus Ef from theshape data (shape profile) obtained by the layer region specifying unit732.

For example, the specifying unit 733 specifies the shape of the fundusEf so that a plurality of shape profiles is smoothly connected. In someembodiments, the specifying unit 733 specifies the shape of the fundusEf by performing linear approximation, curve approximation, or curvedsurface approximation of the same depth position (z position) for theplurality of shape profiles. In some embodiments, the specifying unit733 generates the shape data two-dimensionally or three-dimensionallyrepresenting the shape of the fundus from the plurality of shapeprofiles. In some embodiments, the specifying unit 733 generates anewshape profile two-dimensionally or three-dimensionally representing theshape of the fundus from the plurality of shape profiles. The new shapeprofile is, for example, shape data which is capable of specifying theshape of the fundus using new parameters such as curvature of thefundus, tilt of the fundus, and the like.

(Calculator 74)

The calculator 74 calculates a refractive power obtained by objectivelymeasuring the subject's eye E, and calculates a refractive power of theperipheral region of the region including a fovea of the subject's eye Ebased on the calculated refractive power and the shape of the fundus Efspecified by the specifying unit 733. In some embodiments, thecalculator 74 calculates the refractive power of the peripheral regionof a region including the fovea of the subject's eye based on thecalculated refractive power and a parameter representing opticalcharacteristics of the subject's eye corresponding to the shape of thefundus specified by the specifying unit 733. The calculator 74 can buildan eyeball model based on the parameter representing opticalcharacteristics of the subject's eye corresponding to the shape of thefundus Ef specified by the specifying unit 733, and can calculate therefractive power of the above peripheral region from the built eyeballmodel and the calculated refractive power.

As shown in FIG. 5, the calculator 74 includes a refractive powercalculator 74A, an eyeball model building unit 74B, and a peripheralrefractive power calculator 74C.

(Refractive Power Calculator 74A)

The refractive power calculator 74A calculates the refractive power byprocessing the output from the imaging element of the light receptionsystem of the refractometry unit 20.

In some embodiments, the refractive power calculator 74A executes aprocess of specifying an elliptical shape by elliptically approximatingthe ring pattern image acquired by the imaging element and a process ofobtaining the refractive power (measurement data) based on the specifiedelliptical shape and a diopter for focus adjustment for the focusinglens and the like.

In some embodiments, the refractive power calculator 74A executes aprocess of obtaining brightness distribution in the age in which thering pattern image acquired by the imaging element is depicted, aprocess of obtaining a position of the center of gravity of the ringpattern image from the obtained brightness distribution, a process ofobtaining brightness distribution along a plurality of scanningdirections extending radially from the obtained position of the centerof gravity, a process of specifying a ring pattern image from theobtained brightness distribution along the plurality of scanningdirections, a process of obtaining an approximate ellipse from thespecified ring pattern image, and a process of calculating therefractive power by substituting the major axis and the minor axis ofthe obtained approximate ellipse into a known expression.

In some embodiments, the refractive power calculator 74A executes aprocess of obtaining a deflection (position shift, deformation, etc.)from the reference pattern of the ring pattern image acquired by theimaging element, and a process of obtaining the refractive power fromthis deflection.

In some embodiments, a spherical power S, an astigmatic power C, and anastigmatic axis angle C is calculated as the refractive power. In someembodiments, an equivalent spherical power SE(=S+C/2) is calculated asthe refractive power.

(Eyeball Model Building Unit 74B)

The eyeball model building unit 74B builds an eyeball model. The eyeballmodel building unit 74B can build (form) a new eyeball model by applyingseparately acquired parameters to an eyeball model such as a knownschematic eye.

The eyeball model building unit 74B can build a new eyeball model byapplying an intraocular distance of the subject's eye E acquired by OCTmeasurement or the like as the measured parameter to an eyeball modelsuch as a known schematic eye. In this case, the data processor 70 canexecute calculation processing or the like for obtaining the size (layerthickness, volume, etc.) of the tissue or the distance betweenpredetermined sites. For example, the data processor 70 specifies peakpositions of the detection result (interference signal) of theinterference light corresponding to the predetermined sites in the eyeby analyzing the scan data or the tomographic image, and obtains theintraocular distance based on the distance between the specified peakpositions. In some embodiments, the data processor 70 obtains theintraocular distance (distance between layers) based on the number ofpixels existing between the two layer regions obtained by performingsegmentation processing and a predetermined spacing correction value.The measurement of the intraocular distance is performed along apredetermined direction. The measurement direction of the intraoculardistance may be, for example, a direction determined by OCT scan (forexample, the traveling direction of the measurement light), or adirection determined based on scan data (for example, the directionorthogonal to the layer). Further, the distance data may be distancedistribution data between the two layer regions, a statistic value (forexample, average, maximum value, minimum value, median, mode, variance,standard deviation) calculated from this distance distribution data, ordistance data between representative points of each layer region.Examples of the intraocular distance, which the data processor 70 cancalculate, include an axial length, a corneal thickness, an anteriorchamber depth, a crystalline lens thickness, a length of vitreouscavity, a retinal thickness, a choroidal thickness, and the like.Further, the data processor 70 is capable of calculating variousparameters representing optical characteristics of the eyeball using theobtained intraocular distance.

The specifying unit 733 (or the eyeball model building unit 74B) iscapable of specifying the shape of the fundus Ef using the built eyeballmodel. For example, the specifying unit 733 specifies the shape of thefundus Ef by obtaining a difference between a central region of thefundus Ef and the depth position of the peripheral region.

(Peripheral Refractive Power Calculator 74C)

The peripheral refractive power calculator 74C calculates the refractivepower of the peripheral region outside the region including the fovea inthe fundus Ef. At this time, the peripheral refractive power calculator74C calculates the refractive power of the peripheral region based onthe refractive power of the central region acquired by the refractometryunit 20 and the specified shape of the fundus Ef. The peripheralrefractive power calculator 74C is capable of calculating the refractivepower of the peripheral region using the parameters of the eyeball modelbuilt by the eyeball model building unit 74B.

In some embodiments, the functions of the data processor 70 are realizedby one or more processors. In some embodiments, each function of thealignment processor 71, the displacement specifying unit 72, theanalyzer 73, and the calculator 74 is realized by a single processor. Insome embodiments, the function of each part of the alignment processor71 is realized by a single processor. In some embodiments, the functionof the displacement specifying unit 72 is realized by a singleprocessor. In some embodiments, the function of each part of theanalyzer 73 is realized by a single processor. In some embodiments, thefunction of each part of the calculator 74 is realized by a singleprocessor. In some embodiments, at least part of the data processor 70is provided in the refractometry unit 20 or the OCT unit 30.

(Controller 80)

The controller 80 controls each part of the ophthalmologic apparatus 1.The controller 80 includes a storage unit (now shown), and can storevarious types of information. Examples of the information stored in thestorage unit include a program for controlling each part of theophthalmologic apparatus 1, information of the subject, information ofthe subject's eye, measurement data acquired by the measurement unit 10,processing results by the data processor 70, and the like. The functionsof the controller 80 is realized by a processor.

The controller 80 is capable of controlling a display device (notshown). Upon receiving control of the controller 80, the display devicedisplays information, as a part of user interface. The display devicemay be, for example, a liquid crystal display (LCD), or an organiclight-emitting diode (OLED) display.

The controller 80 can control the ophthalmologic apparatus 1 inaccordance with a signal from an operation device (not shown). Theoperation device functions as a part of the user interface unit. Theoperation device may include various types of hardware keys (thejoystick, buttons, switches, etc.) provided in the ophthalmologicapparatus 1. Further, the operation device may include various types ofperipheral devices (keyboard, mouse, joystick, operation panel, etc.)connected to the ophthalmologic apparatus 1. Further, the operationdevice may include various kinds of software keys (buttons, icons,menus, etc.) displayed on the touch panel.

(Movement Mechanism 90)

The movement mechanism 90 is a mechanism for moving the head unit inupper and horizontal directions and front-back direction, the head unithousing the optical systems (optical systems of the apparatus) such asthe refractometry unit 20, the OCT unit 30, the alignment lightprojection unit 40, the beam splitters BS1 and BS2, and the like. Themovement mechanism 90 can relatively move the measurement unit 10 withrespect to the subject's eye E under the control of the controller 80.For example, the movement mechanism 90 is provided with an actuator thatgenerates driving force for moving the head unit and a transmissionmechanism that transmits the driving force to the head unit. Theactuator is configured by a pulse motor, for example. The transmissionmechanism is configured by a combination of gears, a rack and pinion,and the like, for example. The main controller 80 controls the movementmechanism 90 by sending a control signal to the actuator.

The control for the movement mechanism 90 is used for registration(alignment). For example, the controller 80 obtains a current positionof the measurement unit 10 (optical system of the apparatus). Thecontroller 80 receives information representing the content of themovement control of the movement mechanism 90, and obtains the currentposition of the measurement unit 10. In this case, the controller 80controls the movement mechanism 90 at a predetermined timing (uponstart-up of the apparatus, upon inputting patient information, etc.) tomove the measurement unit 10 to a predetermined initial position.Thereafter, the controller 80 records the control content each time themovement mechanism 90 is controlled. Thereby, a history of the controlcontents can be obtained. As an optical system position obtaining unit,the controller 80 refers to this history, obtains the control contentsup to the present time, and determines the current position of themeasurement unit 10 based on the control contents.

In some embodiments, each time the controller 80 controls the movementmechanism 90, the controller 80 receives the control content andsequentially obtains the current position of the measurement unit 10. Insome embodiments, a position sensor is provided in the ophthalmologicapparatus 1, the position sensor detecting the position of themeasurement unit 10. The controller 80 obtains the current position ofthe measurement unit 10 based on the detection result of the positionsensor.

The controller 80 can control the movement mechanism 90 based on thecurrent position obtained as described above and the movement targetposition determined by the movement target position determining unit71C. Thereby, the measurement unit 10 can be moved to the movementtarget position. For example, the controller 80 obtains a differencebetween the current position and the movement target position. The valueof this difference is a vector value having the current position as astart point and the movement target position as an end point, forexample. This vector value is a three-dimensional vector value expressedin the xyz coordinate system, for example.

In some embodiments, the control for the movement mechanism 90 is usedfor tracking. Here, tracking is to move the optical system of theapparatus according to the movement of the subject's eye E. To performtracking, alignment and focus adjustment are performed in advance. Thetracking is a function of maintaining a suitable positional relationshipin which alignment and focusing are matched by causing the position ofthe optical system of the apparatus and the like to follow the eyemovement.

The OCT unit 30 and the image forming unit 60 are an example of the “OCTunit” according to the embodiments. The imaging unit 100 or the device(a communication interface, an input/output interface, etc.) forreceiving data from the external apparatus or a recording medium is anexample of the “acquisition unit” according to the embodiments. Thecontroller 80, the movement mechanism 90, and the alignment processor 71are an example of the “registration unit” according to the embodiments.The optical system (optical system for performing OCT) included in theOCT unit 30 is an example of the “OCT optical system” according to theembodiments.

<Operation Example>

The operation of the ophthalmologic apparatus 1 according to the presentembodiment will be described.

FIGS. 9 and 10 illustrate an example of the operation of theophthalmologic apparatus 1. FIG. 9 shows a flowchart of an example ofthe operation of the ophthalmologic apparatus 1. FIG. 10 shows aflowchart of an example of the operation of step S3 in FIG. 9. Thestorage unit of the controller 80 stores a of computer programs forrealizing the processing shown in FIGS. 9 and 10. The controller 80operates according to the computer programs, and thereby the controller80 performs the processing shown in FIGS. 9 and 10.

(S1: Perform Alignment)

First, the controller 80 performs alignment.

For example, the controller 80 controls the alignment light projectionunit 40 to project the alignment light onto the subject's eye E. At thistime, a fixation light flux is projected onto the subject's eye E at apredetermined projection position (for example, a projection position onthe measurement optical axis) by a fixation projection system (notshown). For example, the controller 80 specifies a movement amount and amovement direction of the measurement unit 10 from the displacementbetween the pupil center position and the position of the Purkinje imagein the photographic image acquired by the imaging unit 100, and controlsthe movement mechanism 90 based on the specified movement amount and thespecified movement direction to perform registration of the measurementunit 10 with respect to the subject's eye E. The controller 80repeatedly executes this processing until a predetermined alignmentcompletion condition is satisfied.

(S2: Perform Objective Refractometry)

Next, the controller 80 controls the fixation projection system (notshown) to project a fixation target on the measurement optical axis ofthe optical system of the refractometry unit 20 in the fundus Ef(central fixation). After that, the controller 80 controls therefractometry unit 20 to perform objective refractometry in a state inwhich the fixation target is projected on the measurement optical axisof the optical system of the refractometry unit 20.

The refractive power calculator 74A calculate the refractive power ofthe central region including the fovea of the subject's eye E byanalyzing the ring pattern image formed by the reflected light of thelight projected onto the fundus Ef of the subject's eye E.

(S3: Specify Shape of Fundus)

Subsequently, the controller 80 performs the processing for specifyingthe shape of the fundus Ef of the subject's eye E. In the embodiments,the controller 80 controls the OCT unit 30 to perform OCT measurement(OCT scan) in a state in which the fixation target is projected on themeasurement optical axis of the optical system of the refractometry unit20 (OCT unit 30).

In step S3, as described above, the shape data, which represents theshape of the fundus Ef specified so as to cancel the influence of thedisplacement of the measurement unit 10 with respect to the subject'seye E, is acquired. Details of step S3 will be described later.

(S4: Calculate Peripheral Refractive Power)

Subsequently, the controller 80 controls the peripheral refractive powercalculator 74C to calculate the refractive power of the peripheralregion outside the central region including the fovea obtained in stepS2. Therefore, the controller 80 controls the eyeball model buildingunit 74B to build the eyeball model.

Specifically, the eyeball model building unit 74B obtains Height shapedata [pixel] of the predetermined layer region from the data acquired instep S3. The Height data corresponds to a distance in the depthdirection from a predetermined reference position in the tomographicimage. The eyeball model building unit 74B obtains a distance [mm] ofthe Height data using pixel spacing correction value [mm/pixel] which isdefined by the optical system and is specific to the apparatus. Further,the eyeball model building unit 74B builds the eyeball model using theobtained Height data as fundus shape data.

FIG. 11 shows a diagram describing the operation of the eyeball modelbuilding unit 74B according to the embodiments. FIG. 11 schematicallyillustrates a part of parameters of the eyeball model.

The eyeball model building unit 74B builds the eyeball model having apredetermined corneal curvature radius (for example, 7.7 mm) and apredetermined axial length (for example, 24.2 mm) using parameters of aneyeball model such as Gullstrand schematic eye.

The eyeball model building unit 74B sets a pivot point Pv, which isspecific to the apparatus, between the cornea Ec and the fundus Ef inthe eyeball model, as shown in FIG. 11. Typically, a positioncorresponding to a pupil position disposed at a position opticallyconjugate with the optical scanner included in the scan system (forexample, a position of 3 mm apart on the rear side with respect to thecornea Ec) is set as the pivot point Pv. Equidistant (equal optical pathlength) positions (ELS) about the pivot point Pv correspond to flatpositions in the tomographic image obtained by the OCT measurement.

In the eyeball model, the axial length AL and the distance Lp from theanterior surface (posterior surface) of the cornea to the pivot point Pvare known. Therefore, the distance (AL−Lp) from the pivot point Pv tothe fundus Ef is known. When the curvature radius of the fundus Ef isequal to the distance (AL−Lp), the equidistant positions correspond tothe flat positions in the tomographic image as described above. Thereby,the eyeball model building unit 74B can specify the shape (for example,curvature radius) of the fundus Ef from the distance [mm] of theobtained Height data.

Therefore, the eyeball model building unit 74B obtains the difference(fundus shape difference data) Δh [mm] of the height of the peripheralregion with respect to the central region (fovea). The difference Δh maybe obtained for each A line in the tomographic image, or may be obtainedby fitting with an arbitrary function such as a polynomial or anaspheric expression (polynomial including a conic constant).

Next, the peripheral refractive power calculator 74C defines arefractive power of the whole eye system in order to relate the shape ofthe fundus and the refractive power. In a typical eyeball model(Gullstrand schematic eye (precise schematic eye, accommodation pausingstate)), the refractive power of the whole eye system is 58.64[Diopter]. In the air conversion length, the focal length of the wholeeye system is “1000/58.64=17.05” [mm]. Information on unit [mm] obtainedusing the pixel spacing correction value usually represents the distancein tissue of the living body. Thereby, the focal length of the whole eyesystem in tissue of the living body can be calculated by multiplying arefractive index. Assuming that the equivalent refractive index of thewhole eye system is n=1.38, the focal length ft of the whole eye systemin tissue of the living body is “1000/58.64×1.38=23.53” [mm].

The peripheral refractive power calculator 74C calculates the differenceΔD of the eyeball refractive power at the position of the difference Δhof the height of the peripheral region with respect to the centralregion (fovea) according to expression (1). The difference ΔDcorresponds to the difference in the eyeball refractive power relativeto the central region including the fovea.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack & \; \\{{\Delta\; D} = {\frac{1000}{23.53 - {\Delta\; h}} - \frac{1000}{23.53}}} & (1)\end{matrix}$

For example, when Δh=0.1 [mm] (in tissue), ΔD=0.18 [Diopter].

The peripheral refractive power calculator 74C obtains the refractivepower SEp of the peripheral region by applying the difference ΔD ofexpression (1) to the equivalent spherical power SE of the centralregion, as shown in expression (2).[Expression 2]SEp=SE+ΔD  (2)

The peripheral refractive power calculator 74C may obtain the refractivepower of the peripheral region in the tomographic image for each A line,or may obtain by fitting with an arbitrary function.

This terminates the operation of the ophthalmologic apparatus 1 (END).

In step S3 in FIG. 9, processing for specifying the shape of the fundusEf of the subject's eye E is performed as shown in FIG. 10.

(S11: Start Projection Alignment Light)

When the processing of step S3 is started, the controller 80 controlsthe alignment light projection unit 40 to start projecting the alignmentlight onto the subject's eye E.

Also in step S11, in the same manner as in step S1, the fixation lightflux is projected onto the subject's eye E at the predeterminedprojection position (for example, the projection position on themeasurement optical axis) by the fixation projection system (not shown).

(S12: Perform Alignment)

The controller 80 specifies a movement amount and a movement directionof the measurement unit 10 from the displacement between the pupilcenter position and the position of the Purkinje image in thephotographic image acquired by the imaging unit 100, and controls themovement mechanism 90 based on the specified movement amount and thespecified movement direction to perform registration of the measurementunit 10 with respect to the subject's eye E.

(S13: Alignment is Completed?)

The controller 80 determines whether the predetermined alignmentcompletion condition is satisfied. The alignment completion conditionincludes that a position of the optical axis of the measurement unit 10in the x and the y directions coincides with the movement targetposition in the x and the y directions, and that a distance in the zdirection becomes a predetermined working distance. In some embodiments,the working distance is the working distance of the measurement unit 10(objective lens).

When it is determined that the predetermined alignment completioncondition is not satisfied (S13: N), the operation of the ophthalmologicapparatus 1 proceeds to step S12. When it is determined that thepredetermined alignment completion condition is satisfied (S13: Y), theoperation of the ophthalmologic apparatus 1 proceeds to step S14.

(S14: Specify Displacement)

When it is determined that the predetermined alignment completioncondition is satisfied in step S13 (S13: Y), the controller 80 controlsthe displacement specifying unit 72 to specify the displacement betweenthe subject's eye E and the measurement unit 10 from the front image ofthe subject's eye E acquired by the imaging unit 100. That is, thecontroller 80 repeatedly performs alignment until the predeterminedalignment completion condition is satisfied, and then the controller 80controls the displacement specifying unit 72 to specify the displacementbetween the subject's eye E and the measurement unit 10.

(S15: Perform OCT Measurement)

Sequentially, the controller 80 controls the OCT unit 30 to perform OCTscan on a predetermined site in the fundus Ef to perform OCTmeasurement. Examples of the predetermined site include the fovea, theits vicinity, and the like. Examples of the OCT scan include the radialscan, and the like. Thereby, the tomographic image of the central regionincluding the fovea of the fundus Ef can be acquired.

(S16: Correct Tomographic Image)

Next, the controller 80 controls the correction unit 731 to executecorrection processing corresponding to the displacement specified instep S14 on the tomographic image acquired in step S15. For example, thecorrection unit 731 transforms pixel positions of the tomographic imagein the OCT coordinate system into pixel positions in the physicalcoordinate system by performing ray tracing processing on themeasurement light using the optical system model to correct thetomographic image.

(S17: Perform Segmentation Processing)

Next, the controller 80 controls the layer region specifying unit 732 tospecify the predetermined layer region (for example, retinal pigmentepithelium layer) by performing segmentation processing on thetomographic image corrected in step S16. Thereby, the shape data (shapeprofile, etc.) of the predetermined layer region is obtained.

In some embodiments, the OCT measurement (tomographic image acquisitionstep) and the acquisition of the front image of the subject's eye E areperformed in parallel. For example, the front image is acquired duringacquiring the tomographic image. The correction according to thedisplacement (amount of alignment error) at acquisition timing isperformed, for example, for each scan position.

Modification Example

The configuration and the operation of the ophthalmologic apparatusaccording to the embodiments are not limited to the above embodiments.

First Modification Example

In step S4, the eyeball model building unit 74B may build a new eyeballmodel by replacing at least one of the measured data (for example,measured values of axial length, cornea shape, anterior chamber depth,curvature of crystalline lens, thickness of crystalline lens) among theparameters of the eyeball model such as the Gullstrand schematic eye. Insome embodiments, the measured data is obtained from the externalmeasurement apparatus or the electronic health record system. In someembodiments, the axial length, the anterior chamber depth, the curvatureof crystalline lens, and the thickness of crystalline lens are obtainedfrom the scan data acquired by the OCT unit 30.

For example, the peripheral refractive power calculator 74C (or the dataprocessor 70) performs ray tracing processing on a ray incident from thecornea Ec, passing through the pupil, and reaching the fundus Ef, usingthe built new eyeball model (for example, pupil diameter=φ4). In the raytracing processing, a position of the object point is set to a positioncorresponding to a far point obtained from the refractive power(equivalent spherical power SE) in the central region acquired in stepS2. The far distance L from the cornea Ec to the position correspondingto the far point is “−1000/SE” [mm].

First, the peripheral refractive power calculator 74C performs the raytracing processing for the central region. The measured data is appliedto the eyeball model as described above. Therefore, even in the centralregion, the ray may not converge at the fundus Ef. In this case, theperipheral refractive power calculator 74C finely adjusts the parametersof the eyeball model so that the ray converges in the central region(the surface of the fundus Ef is the best image surface).

Next, the peripheral refractive power calculator 74C performs the raytracing processing for the peripheral region using the eyeball modelwhose parameters are finely adjusted (that is, rays having incidentangles with respect to the measurement optical axis passing through arotational point of the eye are traced). The peripheral refractive powercalculator 74C obtains the distance to the object point such that therays converge on the fundus Ef in the peripheral region, by performingray tracing processing while changing the distance to the object point.The obtained distance to the object point corresponds to the far pointdistance Lp in the peripheral region. The peripheral refractive powercalculator 74C can obtain the refract power SEp [Diopter] of theperipheral region using expression (3).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack & \; \\{{SEp} = {- \frac{1000}{Lp}}} & (3)\end{matrix}$

The peripheral refractive power calculator 74C performs ray tracingprocessing while changing the incident angle in a predetermined incidentangle range, and obtains the refractive power SEp of the peripheralregion for each incident angle (angle of view). The refractive power inthe peripheral region may be a discrete value for each incident angle ormay be fitted with an arbitrary function in the incident angle range.

In the present modification examples, the eyeball model is finelyadjusted so that the rays converge at the fundus Ef in the centralregion. Therefore, the obtained refractive power of the peripheralregion corresponds to obtaining a relative refractive power with respectto the central region.

Second Modification Example

In the above embodiments, a tilt angle of the predetermined layer region(for example, retinal pigment epithelium layer, OS-RPE boundary surface)of the fundus with respect to the horizontal direction (a predeterminedreference direction) may be specified from the above shape data, as theshape of the central region of the fundus Ef.

The configuration of the ophthalmologic apparatus according to thesecond modification example is the same as the configuration of theophthalmologic apparatus 1 according to the embodiments except that theeyeball model building unit 74B is omitted. Therefore, the explanationthereof is omitted.

In the present modification example, in step S3, the specifying unit 733(or the peripheral refractive power calculator 74C) calculates a tiltangle θh of the fundus plane for the tomographic image (B scan image) inthe horizontal direction and a tilt angle θv of the fundus plane for theB scan image in the vertical direction, using the Height data obtainedfrom the tomographic image acquired in step S15.

The tilt angles θh and θv can be calculated using the same method as atilt angle g1 as follows.

FIG. 12 schematically shows the tomographic image in the horizontaldirection.

In FIG. 12, at the left end LT of the frame of the tomographic imageIMG, the distance in the vertical direction from the upper end UT of theframe to the image region of the site corresponding to the predeterminedlayer region (layer region specified by the layer region specifying unit732, for example, retinal pigment epithelium layer, OS-RPE boundarysurface, or the nerve fiber layer) in the fundus Ef is set as L1. In thesame manner, at the right end RT of the frame of the tomographic imageIMG, the distance in the vertical direction from the upper end UT of theframe to the image region of the site corresponding to the layer regionis set as R1. The distance L1 is obtained using the Height data at theleft end LT of the frame. The distance R1 is obtained using the Heightdata at the right end RT of the frame. The specifying unit 733 obtains avalue |d| corresponding to the actual dimension for the difference(|R1−L1|) in the vertical direction of the image region of the site atthe left end LT of the frame and the right end RT of the frame in thetomographic image IMG.

Next, the specifying unit 733 obtains a value c corresponding to theactual dimension for the distance H1 in the horizontal direction of theframe of the tomographic image IMG which corresponds to the OCTmeasurement range. For example, the value c is specified using the pixelspacing correction value [mm/pixel] for the length of scanning range inthe horizontal direction.

The specifying unit 733 obtains an inclination angle g0 [degree]according to expression (4).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 4} \right\rbrack & \; \\{{g\; 0} = {\arctan\left( \frac{d}{c} \right)}} & (4)\end{matrix}$

In some embodiments, the specifying unit 733 obtains the tilt angle ofthe fundus plane by correcting the inclination angle g0 according to amisalignment amount between the measurement optical axis and the eyeballoptical axis.

(In the Case that the Measurement Optical Axis and the Eyeball OpticalAxis Substantially Coincide with Each Other)

When the measurement optical axis and the eyeball optical axis (visualaxis) substantially coincide with each other, the specifying unit 733outputs, as the tilt angle g1 of the fundus plane, the inclination angleg0 of the tomographic image without correcting the inclination angle g0as shown in expression (5).

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 5} \right\rbrack & \; \\{{g\; 1} = {{g\; 0} = {{arc}\;{\tan\left( \frac{d}{c} \right)}}}} & (5)\end{matrix}$(In the Case that the Eyeball Optical Axis is Shifted with Respect tothe Measurement Optical Axis)

When the eyeball optical axis is shifted with respect to the measurementoptical axis, the specifying unit 733 obtains the tilt angle g1 of thefundus plane by correcting the inclination angle g0 of the tomographicimage based on a shift amount.

For example, the specifying unit 733 obtains a correction angle φ1according to a linear expression with the shift amount ds as variableshown in expression (6), and then obtains the tilt angle g1 of thefundus plane by correcting the inclination angle g0 using the obtainedcorrection angle φ1 as shown in expression (7). In expression (6), α1and c1 are constants. For example, α1 and c1 can be obtained using theschematic eye data.[Expression 6]φ1=α1×ds+c1  (6)[Expression 7]g1=g0−φ1  (7)(In the Case that the Eyeball Optical Axis is Tilted with Respect to theMeasurement Optical Axis)

When the eyeball optical axis is tilted with respect to the measurementoptical axis, the specifying unit 733 obtains the tilt angle g1 of thefundus plane by correcting the inclination angle g0 of the tomographicimage based on a tilt amount.

For example, the specifying unit 733 obtains a correction angle φ2according to a linear expression with the tilt amount dt as variableshown in expression (8), and then obtains the tilt angle g1 of thefundus plane by correcting the inclination angle g0 using the obtainedcorrection angle φ2 as shown in expression (9). In expression (8), α2and c2 are constants. For example, α2 and c2 can be obtained using theschematic eye data.[Expression 8]φ2=α2×dt+c2  (8)[Expression 9]g1=g0−φ2  (9)(In the Case that the Eyeball Optical Axis is Shifted and Tilted withRespect to the Measurement Optical Axis)

When the eyeball optical axis is shifted and tilted with respect to themeasurement optical axis, the specifying unit 733 obtains the tilt angleg1 of the fundus plane by correcting the inclination angle g0 of the Bscan image based on the shift amount and the tilt amount.

For example, in a range where the shift amount ds and the tilt amount dtare small, the specifying unit 733 obtains a correction angle φ3according to an expression with the shift amount ds and the tilt amountdt as variables shown in expression (10), and then obtains the tiltangle g1 of the fundus plane by correcting the inclination angle g0using the obtained correction angle φ3 as shown in expression (11). Insome embodiments, expression (10) is a combining expression obtained bylinearly combined an expression for obtaining the correction angle ofthe shift amount and an expression for obtaining the correction angle ofthe tilt amount. In expression (10), α3, α4 and c3 are constants. Forexample, α3, α4, and c3 can be obtained using the schematic eye data.[Expression 10]φ3=α3×ds+α4×dt+c3  (10)[Expression 11]g1=g0−φ3  (11)

In the present modification example, for horizontal and verticaldirections respectively, the refractive power calculator 74A correctsthe ring pattern image obtained in step S2 in accordance with the tiltangles θh and θv of the fundus plane specified as described above. Therefractive power calculator 74A performs ellipse approximation on thecorrected ring pattern image, and obtains the refractive power using theobtained elliptical shape by a known method. The obtained refractivepower is calculated as the refractive power of the central region.

For example, a major axis of the ring pattern image is LA, and a minoraxis of the ring pattern image is LB, the ring pattern image beingacquired when the tilt angle of the fundus plane is 0 degree. When thefundus plane is tilted in the major axis direction and the tilt angle isθ degree, the major axis of the ellipse approximated from the acquiredring pattern image is LA/cos θ, and the minor axis is LB. Therefore, therefractive power calculator 74A can correct the ring pattern image bymultiplying cos θ in the major axis direction of the ellipse obtained byapproximating the ring pattern image acquired in step S2. The sameapplies to the case of tilting in the minor axis direction. For example,the refractive power calculator 74A can correct the ring pattern imageby obtaining the tilt angle in the major axis direction of the ellipseand the tilt angle in the minor axis direction of the ellipse from eachof the tilt angles in the horizontal and vertical directions.

In the same manner as the above embodiments, the peripheral refractivepower calculator 74C obtains the refractive power SEp of the peripheralregion by applying the difference ΔD of expression (1) to the equivalentspherical power SE of the central region, as shown in expression (2).

Third Modification Example

In the above embodiments or the modification examples thereof, the casein which the tomographic image of the subject's eye E is corrected basedon the displacement of the measurement unit 10 (measurement opticalaxis) with respect to the subject's eye E, and the shape datarepresenting the shape of the fundus Ef is obtained from the correctedtomographic image has been described. However, the configuration of theophthalmologic apparatus 1 according to the embodiments is not limitedto this. For example, the shape data representing the shape of thefundus Ef specified from the tomographic image of the subject's eye Emay be corrected based on the displacement of the measurement unit 10(measurement optical axis) with respect to the subject's eye E.

In the following, the ophthalmologic apparatus according to the fourthmodification example will be described focusing on differences from theophthalmologic apparatus 1 according to the embodiments.

The configuration of the ophthalmologic apparatus of the fourthmodification example is the same as that of the ophthalmologic apparatus1 according to the embodiments.

The ophthalmologic apparatus according to the fourth modificationexample is capable of operating as shown in FIG. 9. The ophthalmologicapparatus according to the fourth modification example is capable ofoperating as follow, in step S3 of FIG. 9.

FIG. 13 shows an example of the operation of the ophthalmologicapparatus 1 according to the fourth modification example. FIG. 13 showsa flowchart of an example of the operation of the ophthalmologicapparatus 1. The storage unit of the controller 80 stores a of computerprograms for realizing the processing shown in FIG. 13. The controller80 operates according to the computer programs, and thereby thecontroller 80 performs the processing shown in FIG. 13.

That is, in the present modification example, in step S3 in FIG. 9,processing for specifying the shape of the fundus Ef of the subject'seye E is performed as shown in FIG. 13.

(S21: Start Projection Alignment Light)

When the processing of step S3 is started, the controller 80 controlsthe alignment light projection unit 40 to start projecting the alignmentlight onto the subject's eye E in the same manner as in step S11.

(S22: Perform Alignment)

The controller 80 controls the movement mechanism 90 to performregistration of the measurement unit 10 with respect to the subject'seye E in the same manner as in step S12.

(S23: Alignment is Completed?)

The controller 80 determines whether the predetermined alignmentcompletion condition is satisfied in the same manner as in step S13.

When it is determined that the predetermined alignment completioncondition is not satisfied (S23: N), the operation of the ophthalmologicapparatus according to the present modification example proceeds to stepS22. When it is determined that the predetermined alignment completioncondition is satisfied (S23: Y), the operation of the ophthalmologicapparatus according to the present modification example proceeds to stepS24.

(S24: Specify Displacement)

When it is determined that the predetermined alignment completioncondition is satisfied in step S23 (S23: Y), the controller 80 controlsthe displacement specifying unit 72 to specify the displacement betweenthe subject's eye E and the measurement unit 10 in the same manner as instep S14.

(S25: Perform OCT Measurement)

Sequentially, the controller 80 controls the OCT unit 30 to perform OCTscan on a predetermined site in the fundus Ef to perform OCT measurementin the same manner as in step S15.

(S26: Perform Segmentation Processing)

Next, the controller 80 controls the layer region specifying unit 732 tospecify the predetermined layer region (for example, retinal pigmentepithelium layer) by performing segmentation processing on thetomographic image corrected in step S25. Thereby, the shape data (shapeprofile, etc.) of the predetermined layer region is obtained.

(S27: Correct Shape Data)

Next, the controller 80 controls the correction unit 731 to executecorrection processing corresponding to the displacement specified instep S24 on the shape data acquired in step S26. For example, thecorrection unit 731 transforms pixel positions of the shape data (shapeprofile) in the OCT coordinate system into pixel positions in thephysical coordinate system by performing ray tracing processing on themeasurement light using the optical system model to correct the shapedata.

This terminates the operation of the ophthalmologic apparatus accordingto the present modification example (END).

[Effects]

The ophthalmologic apparatus and the method of controlling theophthalmologic apparatus according to the embodiments are explained.

An ophthalmologic apparatus (1) according to some embodiments includesan OCT unit (30, image forming unit 60), an acquisition unit (imagingunit 100), and a specifying unit (733). The OCT unit is configured toacquire a tomographic image of a subject's eye (E) using opticalcoherence tomography. The acquisition unit is configured to acquire afront image of the subject's eye. The specifying unit is configured tospecify shape of a tissue of the subject's eye based on the tomographicimage acquired by the OCT unit and the front image acquired by theacquisition unit.

According to such a configuration, the influence of the displacementbetween the subject's eye and the optical system for measuring the shapeof the tissue can be reduced from information obtained from thetomographic image of the subject's eye and the front image (for example,anterior segment image) of the subject's eye. Thereby, the shape of thetissue of the subject's eye can be specified with high reproducibilityand high accuracy.

The ophthalmologic apparatus according to some embodiments include aregistration unit (controller 80, movement mechanism 90, and alignmentprocessor 71) configured to perform registration between the subject'seye and the OCT unit, and a displacement specifying unit (72) configuredto specify a displacement between the subject's eye and the OCT unitbased on the front image of the subject's eye acquired by theacquisition unit after registration performed by the registration unit,wherein the specifying unit specifies the shape of the tissue based onthe displacement specified by the displacement specifying unit.

According to such a configuration, the displacement between thesubject's eye and the OCT unit is specified after registration, and theshape of the tissue of the subject's eye is specified based on thespecified displacement. Thereby, the shape of the tissue of thesubject's eye can be specified with high reproducibility and highaccuracy, without being affected by the displacement between thesubject's eye and the OCT unit.

In the ophthalmologic apparatus according to some embodiments, thespecifying unit includes a correction unit (731) configured to correctthe tomographic image based on the displacement specified by thedisplacement specifying unit, and a layer region specifying unit (732)configured to specify a predetermined layer region in the tomographicimage corrected by the correction unit, and the specifying unit obtainsshape data representing a shape of the predetermined layer region.

According to such a configuration, by correcting the tomographic imagebased on the specified displacement, specifying the predetermined layerregion in the corrected tomographic image, and generating the shape datarepresenting the shape of the specified layer region, the shape of thetissue can be specified. Thereby, the shape of the tissue of thesubject's eye can be specified with simple processing, highreproducibility and high accuracy.

In the ophthalmologic apparatus according to some embodiments, thespecifying unit includes a layer region specifying unit (732) configuredto specify a predetermined layer region in the tomographic image, and acorrection unit (731) configured to correct shape data representing ashape of the predetermined layer region specified by the layer regionspecifying unit, based on the displacement specified by the displacementspecifying unit.

According to such a configuration, by specifying the predetermined layerregion in the tomographic image, and correcting the shape datarepresenting the shape of the specified layer region based on the abovedisplacement, the shape of the tissue can be specified. Thereby, theshape of the tissue of the subject's eye can be specified with simpleprocessing, high reproducibility and high accuracy.

In the ophthalmologic apparatus according to some embodiments, thecorrection unit includes a ray tracing processor (731A) that performsray tracing processing on the basis of the displacement specified by thedisplacement specifying unit on measurement light for performing opticalcoherence tomography and that obtains a coordinate position in apredetermined coordinate system corresponding to a position on the rayof measurement light, and a coordinate transforming unit (731B) thatcorrects the tomographic image or the shape data based on the obtainedcoordinate position.

According to such a configuration, the position after transformation isobtained by performing ray tracing processing on the basis of thedisplacement specified by the displacement specifying unit on themeasurement light, and the tomographic image or the shape data iscorrected by performing coordinate transformation. Thereby, the shape ofthe tissue of the subject's eye can be specified with simple processing,high reproducibility and high accuracy.

In the ophthalmologic apparatus according to some embodiments, thecorrection unit corrects the tomographic image or the shape data basedon correction information and the displacement specified by thedisplacement specifying unit, the correction information being obtainedin advance by performing ray tracing processing on the basis of two ormore displacements on measurement light for performing optical coherencetomography.

According to such a configuration, the tomographic image or the shapedata is corrected in accordance with the displacement specified by thedisplacement specifying unit by performing ray tracing processing on thebasis of two or more displacements in advance. Thereby, the shape of thetissue of the subject's eye can be specified with simple processing,high reproducibility and high accuracy.

The ophthalmologic apparatus according to some embodiments includes analignment light projection unit (40) configured to project alignmentlight onto the subject's eye. Wherein the displacement specifying unitspecifies the displacement based on a position of an image (Purkinjeimage) based on the alignment light in the front image and acharacteristic position (pupil center position) of the subject's eye.

According to such a configuration, the tomographic image or the shapedata is corrected based on the displacement between the position of thePurkinje image and the characteristic position of the subject's eye.Thereby, the influence of displacement between the subject's eye and theOCT unit can be reduced while using the existing optical system, and theshape of the tissue of the subject's eye can be specified with highreproducibility and high accuracy.

In the ophthalmologic apparatus according to some embodiments, the shapeof the tissue is a shape of the fundus.

According to such a configuration, the shape of the tissue of thesubject's eye can be specified with high reproducibility and highaccuracy, without being affected by the displacement between thesubject's eye and the OCT unit.

The ophthalmologic apparatus according to some embodiments includes acalculator (peripheral refractive power calculator 74C) calculates arefractive power of a peripheral region of a region including a fovea ofthe subject's eye based on a refractive power obtained by objectivelymeasuring the subject's eye and parameter representing opticalcharacteristics of the subject's eye corresponding to the shape of thefundus specified by the specifying unit.

According such a configuration, in accordance with the shape of thefundus of the subject's eye, the refractive power of the peripheralregion of the region including the fovea can be obtained with highaccuracy.

In the ophthalmologic apparatus according to some embodiments, the shapeof the fundus includes a tilt angle of a predetermined layer region inthe fundus with respect to a predetermined reference direction.

According to such a configuration, in accordance with the tilt angle ofthe predetermined layer region in the fundus with respect to thepredetermined reference direction, the refractive power of theperipheral region of the region including the fovea can be obtained withhigh accuracy.

A method of controlling an ophthalmologic apparatus according to someembodiments, the method including a tomographic image acquisition stepthat acquires a tomographic image of a subject's eye (E) using opticalcoherence tomography, a front image acquisition step that acquires afront image of the subject's eye, and a specifying step that specifiesshape of a tissue of the subject's eye based on the tomographic imageacquired in the tomographic image acquisition step and the front imageacquired in the front image acquisition step.

According to such a method, the influence of the displacement betweenthe subject's eye and the optical system for measuring the shape of thetissue can be reduced from information obtained from the tomographicimage of the subject's eye and the front image (for example, anteriorsegment image) of the subject's eye. Thereby, the shape of the tissue ofthe subject's eye can be specified with high reproducibility and highaccuracy.

The method of controlling the ophthalmologic apparatus according to someembodiments further includes a registration step that performsregistration between the subject's eye and an OCT optical system forperforming optical coherence tomography, and a displacement specifyingstep that specifies a displacement between the subject's eye and the OCToptical system based on the front image of the subject's eye acquired inthe front acquisition step after registration in the registration step,wherein the specifying step specifies the shape of the tissue based onthe displacement specified in the displacement specifying step.

According to such a method, the displacement between the subject's eyeand the OCT optical system is specified after registration, and theshape of the tissue of the subject's eye is specified based on thespecified displacement. Thereby, the shape of the tissue of thesubject's eye can be specified with high reproducibility and highaccuracy, without being affected by the displacement between thesubject's eye and the OCT optical system.

In the method of controlling the ophthalmologic apparatus according tosome embodiments, the specifying step includes a correction step thatcorrects the tomographic, image based on the displacement specified inthe displacement specifying step, and a layer region specifying stepthat specifies a predetermined layer region in the tomographic imagecorrected in the correction step, and the specifying step obtains shapedata representing a shape of the predetermined layer region based on theshape of the predetermined layer region.

According to such a method, by correcting the tomographic image based onthe specified displacement, specifying the predetermined layer region inthe corrected tomographic image, and generating the shape datarepresenting the shape of the specified layer region, the shape of thetissue can be specified. Thereby, the shape of the tissue of thesubject's eye can be specified with simple processing, highreproducibility and high accuracy.

In the method of controlling the ophthalmologic apparatus according tosome embodiments, the specifying step includes a layer region specifyingstep that specifies a predetermined layer region in the tomographicimage, and a correction step that corrects shape data representing ashape of the predetermined layer region specified in the layer regionspecifying step, based on the displacement specified in the displacementspecifying step.

According to such a method, by specifying the predetermined layer regionin the tomographic image, and correcting the shape data representing theshape of the specified layer region based on the above displacement, theshape of the tissue can be specified. Thereby, the shape of the tissueof the subject's eye can be specified with simple processing, highreproducibility and high accuracy.

<Others>

The above-described embodiments are merely examples for carrying out thepresent invention. Those who intend to implement the present inventioncan apply any modification, omission, addition, or the like within thescope of the gist of the present invention.

In some embodiments, a program for causing a computer to execute themethod of controlling the ophthalmologic apparatus is provided. Such aprogram can be stored in any kind of recording medium that can be readby the computer. Examples of the recording medium include asemiconductor memory, an optical disk, a magneto-optical disk (CD-ROM,DVD-RAM, DVD-ROM, MO, etc.), a magnetic storage medium (hard disk,floppy (registered trade mark) disk, ZIP, etc.), and the like. Thecomputer program may be transmitted and received through a network suchas the Internet, LAN, etc.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. An ophthalmologic apparatus comprising: an OCT unit including an OCT scanner and configured to acquire a tomographic image of a subject's eye using optical coherence tomography; an acquisition unit including circuitry configured to capture or receive a front image of the subject's eye; processing circuitry configured as a specifying unit configured to specify shape of a tissue of the subject's eye based on the tomographic image acquired by the OCT unit and the front image acquired by the acquisition unit; the processing circuitry further configured as a registration unit to perform registration between the subject's eye and the OCT unit; and the processing circuitry further configured as a displacement specifying unit that specifies a displacement between an eyeball optical axis of the subject's eye and a measurement optical axis of the OCT unit based on the front image of the subject's eye acquired by the acquisition unit after registration is performed by the registration unit, wherein the specifying unit is further configured to specify the shape of the tissue based on the displacement specified by the displacement specifying unit, generate an optical system model based on a biometric data of the subject's eye and the displacement specified by the displacement specifying unit, correct the tomographic image based on the displacement specified by the displacement specifying unit, specify a predetermined layer region in the tomographic image corrected by the correction unit, obtain shape data representing a shape of the predetermined layer region, perform ray tracing processing on measurement light for performing optical coherence tomography using the generated optical system model, and obtain a coordinate position in a predetermined coordinate system corresponding to a position on a ray of measurement light, and correct the tomographic image or the shape data based on the obtained coordinate position by transforming pixel positions of the tomographic image into pixel positions in the predetermined coordinate system.
 2. The ophthalmologic apparatus of claim 1, wherein the specifying unit corrects the tomographic image or the shape data based on correction information and the displacement specified by the displacement specifying unit, the correction information being obtained in advance by performing ray tracing processing on the basis of two or more displacements on measurement light for performing optical coherence tomography.
 3. The ophthalmologic apparatus of claim 1, further comprising: an alignment light projection unit including a light source and configured to project alignment light onto the subject's eye, wherein the displacement specifying unit specifies the displacement based on a position of an image based on the alignment light in the front image and a characteristic position of the subject's eye.
 4. The ophthalmologic apparatus of claim 1, wherein the shape of the tissue is a shape of a fundus.
 5. The ophthalmologic apparatus of claim 4, wherein: the processing circuitry is further configured as a calculator that calculates a refractive power of a peripheral region of a region including a fovea of the subject's eye based on a refractive power obtained by objectively measuring the subject's eye and parameter representing optical characteristics of the subject's eye corresponding to the shape of the fundus specified by the specifying unit.
 6. The ophthalmologic apparatus of claim 5, wherein the shape of the fundus includes a tilt angle of a predetermined layer region in the fundus with respect to a predetermined reference direction.
 7. A method of controlling an ophthalmologic apparatus, the method comprising: a tomographic image acquisition step that acquires a tomographic image of a subject's eye using optical coherence tomography; a front image acquisition step that acquires a front image of the subject's eye; a specifying step that specifies shape of a tissue of the subject's eye based on the tomographic image acquired in the tomographic image acquisition step and the front image acquired in the front image acquisition step; a registration step that performs registration between the subject's eye and an OCT optical system for performing optical coherence tomography; and a displacement specifying step that specifies a displacement between an eyeball optical axis of the subject's eye and a measurement optical axis of the OCT optical system based on the front image of the subject's eye acquired in the front acquisition step after registration in the registration step, wherein the specifying step further includes specifying the shape of the tissue based on the displacement specified in the displacement specifying step, generating an optical system model based on a biometric data of the subject's eye and the displacement specified by the displacement specifying step, correcting the tomographic image based on the displacement specified in the displacement specifying step, specifying a predetermined layer region in the tomographic image corrected in the correcting, obtaining shape data representing a shape of the predetermined layer region based on the shape of the predetermined layer region, and performing ray tracing processing using the generated optical system model and to correct the tomographic image or the shape data by transforming pixel positions of the tomographic image into pixel positions in a predetermined coordinate system.
 8. An ophthalmologic apparatus comprising: an OCT unit including an OCT scanner and configured to acquire a tomographic image of a subject's eye using optical coherence tomography; an acquisition unit including circuitry configured to capture or receive a front image of the subject's eye; processing circuitry configured as a specifying unit configured to specify shape of a tissue of the subject's eye based on the tomographic image acquired by the OCT unit and the front image acquired by the acquisition unit; the processing circuitry further configured as a registration unit to perform registration between the subject's eye and the OCT unit; and the processing circuitry further configured as a displacement specifying unit that specifies a displacement between an eyeball optical axis of the subject's eye and a measurement optical axis of the OCT unit based on the front image of the subject's eye acquired by the acquisition unit after registration is performed by the registration unit, wherein the specifying unit is further configured to specify the shape of the tissue based on the displacement specified by the displacement specifying unit, generate an optical system model based on a biometric data of the subject's eye and the displacement specified by the displacement specifying unit, specify a predetermined layer region in the tomographic image, correct shape data representing a shape of the predetermined layer region based on the displacement specified by the displacement specifying unit, perform ray tracing processing based on the displacement specified by the displacement specifying unit on measurement light for performing optical coherence tomography and using the generated optical system model and to correct the tomographic image or the shape data by transforming pixel positions of the tomographic image into pixel positions in a predetermined coordinate system to a position on the ray of measurement light, and correct the tomographic image of the shape data based on the obtained coordinate position.
 9. A method of controlling an ophthalmologic apparatus, the method comprising: a tomographic image acquisition step that acquires a tomographic image of a subject's eye using optical coherence tomography; a front image acquisition step that acquires a front image of the subject's eye; a specifying step that specifies shape of a tissue of the subject's eye based on the tomographic image acquired in the tomographic image acquisition step and the front image acquired in the front image acquisition step; a registration step that performs registration between the subject's eye and an OCT optical system for performing optical coherence tomography; and a displacement specifying step that specifies a displacement between an eyeball optical axis of the subject's eye and a measurement optical axis of the OCT optical system based on the front image of the subject's eye acquired in the front acquisition step after registration in the registration step, wherein the specifying step further includes specifying the shape of the tissue based on the displacement specified in the displacement specifying step, generating an optical system model based on a biometric data of the subject's eye and the displacement specified by the displacement specifying step, specifying a predetermined layer region in the tomographic image, correcting shape data representing a shape of the predetermined layer region based on the displacement specified by the displacement specifying step, and performing ray tracing processing using the generated optical system model and to correct the tomographic image or the shape data by transforming pixel positions of the tomographic image into pixel positions in a predetermined coordinate system. 